A major nutritional problem in the United States today is obesity. Obesity generally results from the consumption of more calories than are expended, and fats contribute from 30% to 40% of the calories consumed by most Americans. Consumption of fat contributes to human disease states, such as heart and coronary disease. One method of reducing obesity and/or diseases such as heart and coronary diseases in the human population is to reduce the consumption of fat. In recent years, fat substitutes or low-calorie fats have attracted increasing attention as a method of reducing the fat and calorie content of foodstuffs. The objective is to provide edible fats with reduced absorption and digestive properties with minimal side effects and with acceptable taste and feel characteristics when incorporated into food compositions.
Transesterification reactions have been used to prepare saccharide fatty acid polyesters which have reduced absorption and digestive properties. Such transesterification reactions generally required high temperatures and/or toxic solvents (such as dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, and the like) and were not, therefore generally suitable for the preparation of fat substitutes for use in food applications. Another method for the production of sucrose fatty acid esters is the "micro-emulsion" process. A drawback of that process is that it is difficult to remove the solvent used while maintaining the micro-emulsion state. In addition, large quantities of soap are also required to produce stable micro-emulsions.
Rizzi et al., U.S. Pat. No. 3,963,699 (issued Jun. 15, 1976), provided a solvent-free process for the production of saccharide fatty acid polyesters. The method involved heating sucrose, fatty acid lower alkyl esters, an alkali metal fatty acid soap, and a basic catalyst to form a homogeneous melt at 185.degree. C. or greater. Thereafter, excess fatty acid lower alkyl esters are added in the second step to the reaction product of the first step. One drawback to this method is that after only a few moments at 185.degree. C. or above, sucrose begins to decompose which leads to undesirable by-products. Another drawback is that this reaction mixture of Rizzi et al. is heterogeneous due to the mutual insolubility of sucrose and the fatty acid lower alkyl esters.
Akok and Swanson, 55 J. Food Sci., 236 (1990), employed sucrose octaacetate rather than sucrose in a transesterification reaction. Sucrose octaacetate has increased solubility in the fatty acid ester reactants and, therefore, provides a more homogeneous reaction system along with better yields of the sucrose fatty acid polyester and lighter colored products (i.e. reduced caramelization and other decomposition reactions.) This method results in the generation of large amounts of non-fatty acid-containing ester. (Eight moles of methyl acetate are produced for each mole of sucrose octaacetate reacted.) Methyl acetate is a highly flammable material which generally must be either disposed of in an environmentally acceptable manner or converted to acetic acid for reuse or recycling.
Yamamoto et al., U.S. Pat. No. 4,611,055 (issued Sep. 9, 1986), provided a method whereby the sucrose fatty acid esters are purified by subjecting the acidified reaction product to molecular distillation whereby the sucrose fatty acid polyesters are recovered as the residue. In the reaction, Yamamoto et al. called for a molten mixture of sucrose, a fatty acid lower alkyl ester, a basic transesterification catalyst, and a fatty acid alkali metal soap at a temperature from 120.degree. to 180.degree. C. under a vacuum less than 10 mm Hg with stirring. In that reaction, the fatty acid alkali metal soap is used to insure a homogeneous reaction mixture. Such fatty acid metal soap is not used or required in the Meyer et al. method discussed below.
More recently, Meyer et al., U.S. Pat. No. 4,840,815 (issued Jun. 20, 1989) and Meyer et al., PCT Publication WO 92/03060 (published Mar. 5, 1992), provided a one-stage, solvent-free, low-temperature, low-pressure process for the preparation of saccharide fatty acid polyesters. The Meyer et al. process involves reacting a mixture of a lower acyl ester saccharide, a fatty acid lower alkyl ester, and an alkali metal catalyst at a reaction temperature of 100.degree. to 125.degree. C. while drawing a vacuum of less than about 15 torr over the reaction mixture. The saccharide fatty acid polyesters are reported to be formed via a transesterification reaction whereby at least a portion of the lower acyl ester groups on the starting saccharide are replaced with the fatty acid groups from the fatty acid lower alkyl ester. The transesterification catalysts employed were alkali metals, with sodium and potassium metals the most preferred. At the reaction temperature, the alkali metal catalysts were molten.
The assignee of the present application has filed two other applications each entitled, "Improved Method for Preparing Saccharide Fatty Acid Polyesters By Transesterification," Ser. Nos.: 08/132,106, filed Oct. 5, 1993 and 08/132,497, filed Oct. 5, 1993. Those applications are incorporated by reference here. Those applications disclose reactions for generating saccharide fatty acid polyesters, although they have the drawback that removal of by-products is not as effective as desired. The instant invention comprises the further inventive step of requiring the use of thin film reaction methodology to facilitate removal of the non-fatty acid-containing ester and/or alcohol by-products, thereby increasing the efficiency of the reaction to produce polyol fatty acid polyesters.
It is desirable to provide a new method for the production of polyol fatty acid polyesters, especially sucrose fatty acid polyesters, which overcomes some of the problems encountered in the prior art. It is also desirable to provide a new method for the production of polyol fatty acid polyesters, especially sucrose fatty acid polyesters, which results in less caramelization and/or decomposition products and which generates reduced amounts of by-product low molecular weight esters and/or alcohols. The methods of the present invention are generally easier to use and provide better polyol fatty acid polyesters than the methods of the prior art. The methods of the present invention generally result in less caramelization and better yields of the polyol fatty acid polyesters as the reaction by-products are removed more efficiently in a thin film reaction, thereby resulting in more efficient formation of polyol fatty acid polyester by forcing the fatty acid esterification equilibrium reaction towards completion.